Jiangying Wu

A high-resolution stalagmite record of the Holocene East Asian monsoon from Mt Shennongjia, central China

High-resolution oxygen isotope (δ18O) profiles of six stalagmites from Sanbao Cave in Hubei province, central China, established with 1413 oxygen isotope data and 65 230Th ages, provide a continuous history of East Asian Summer Monsoon (EASM) intensity for the period from 13—0.2 thousand years before present (ky BP, relative to AD 1950). The δ 18O record includes four distinct stages in the evolution of the EASM: (1) an abrupt transition (~11.5 ky BP) into the Holocene; (2) a period of gradual increase in monsoon intensity (11.5—9.5 ky BP); (3) the maximum humid period (9.5—6.5 ky BP); and (4) a period of gradual decline in monsoon intensity (6.5—0.2 ky BP). Comparison of Sanbao with regional records of comparable resolution reveals that the timing of the beginning and end of the Holocene Optimum (as defined by the minimum in δ18 O) was similar in the Indian and East Asian monsoon systems. This supports the idea that shifts in the monsoon tied to shifts in the mean position of the Inter-Tropical Convergence Zone (ITCZ) may control monsoon intensity throughout the entire low-latitude region of Asia on orbital timescales. This observation also supports the idea that the fluctuations in δ18 O recorded across southern Asia reflect broad changes in the monsoon, as opposed to local meteoric precipitation. The EASM records from Sanbao largely follow orbital-scale insolation changes, yet exhibit similar variability to Greenland ice core δ18O on millennial to centennial scales during the early to middle Holocene (r = 0.94).

A continuous 3000-year precipitation record of ENSO variability during LGM from a stalagmite in Nanjing

A glacial stalagmite chronology from Nanjing has been established by the TIMS-U series dating and annual band counting methods. The annually layering sequence spanning the 3000-year period from 18179 to 14900 calendar years before the present (aBP) was analyzed for evidence of East Asian summer monsoon precipitation variability during the Last Glacial Maximum (LGM). Power spectral analysis of the sequence shows a distinct interannual (2-7 years) band of enhanced variability suggestive of El Niño-Southern Oscillation (ENSO) teleconnections into East China during the LGM when climatic boundary conditions were different from those of today. The lower frequency bands (4-7 years) variability becomes weaker from 18179 to 14900 aBP, supporting the precession forcing model. The reappearance of the ENSO band in the coldest climatic boundary conditions during the Heinrich Event 1, however, suggests the stimulation of the enhanced East Asia winter monsoon to the El Niño events.

A quick cooling event of the East Asian monsoon responding to Heinrich event 1: Evidence from stalagmite δ18O records

Based on TIMS U-series dating results and annual band counting method, an annual-resolution time scale from 17450 to 14420 aBP has been established for a stalagmite from the Hulu Cave at Tangshan, Nanjing. A high-resolution oxygen isotopic record reveals decadral-centural oscillations in air temperature in the East Asian monsoon climate area during the last glacial maximum. The most conspicuous feature in the oxygen isotopic record in the period is the particular cold event synchronized with the last Heinrich event (H1) in the northern Atlantic deep-sea records. This particular cold event, beginning at 16140 ± 100 aBP, shows a rapid cooling down with a magnitude of 7–8°C in air temperature within 36 years. Furthermore, δ18O record demonstrates that the event lasted 790 years with gradually warming tendency (10 cycles of air temperature oscillations) after the remarkable cooling down. We believed that this unique pattern of event recorded in the stalagmite δ8O might be controlled by various factors including changes of insolation at mid-latitude Northern Hemisphere, the southern extend of the last ice-rafted event in the North Atlantic and changes of the Equatorial Pacific sea surface temperature.